We previously reported experimental evidence that uteroglobin (UG) in conjunction with transglutaminase (TG) can mask the antigenicity of implanting rabbit embryos as well as epididymal sperm. Although the mechanism of action of uteroglobin and transglutaminase had been hypothesized no experimental data were available at that time. We have now carried out experiments with epididymal spermatozoa and prostatic fluid and a crosslinked molecule (sperm protein-UG) could be visualized in SDS-PAGE. This hybrid molecule may be the crosslinked form between surface antigens and uteroglobin. In collaboration with Dr. Schiffman and his associates we have shown that uteroglobin in micromolar concentration inhibits chemotoxis of neutrophils as well as monocytes. This may suggest yet another function of UG on the rabbit immune system and explain why the implanting embryo as well as spermatozoa do not normally elicit immune response in the female mammal.